Current methods of forming GaAs thin film solar cells from GaAs or Ge substrates via epitaxial lift-off are relatively expensive, due at least in part to the cost of the substrates used and the inefficient lift-off process using etching of a sacrificial layer.
One of the current approaches for producing high-efficiency III-V solar cells on low-cost substrates involves the lattice-matched epitaxial growth on a germanium or GaAs single crystal substrate and the use of a sacrificial layer to perform epitaxial lift-off via selective etching of the sacrificial layer, followed by transfer of the device to a low-cost substrate. Unfortunately, the reuse of the very expensive substrate is problematic, due to the need for chemical etching of a sacrificial layer. An alternative approach involves the use of a low-cost substrate (e.g., crystalline Si, glass, or metal film) with a complex buffer layer to accommodate the strain caused by the lattice mismatch between the III-V film and the underlying substrate. However, both of these approaches suffer from various deficiencies, including but not limited to complexity and cost. Accordingly, improved techniques for thin film growth and lift-off are desired.